1. Field of the Invention
The present invention relates to a process for preparing an extrudable product, suitable for forming into a chewable pet food and comprising between about 56% to about 80% dry wheat gluten mix, between about 9% to about 28% liquid plasticizer mix and between about 8% to about 18% moisture by weight of the product. The invention further relates to the extrudable product prepared by that process. The invention also relates to a process for preparing a chewable pet food from the extrudable product and additionally relates to the chewable pet food.
2. Related Art
It is well known to produce products from wheat gluten and plasticizers. Wheat gluten is used in certain products as it imparts elasticity to the product. However, there are difficulties in processing wheat gluten and in particular controlling the processing flowability. U.S. Pat. No. 5,665,152 discloses a method of forming a biodegradable article from a formulation comprising, among other components, a grain protein such as wheat gluten, starch, a plasticizer and a reducing agent. The formulation is pelleted by extrusion processing at temperatures of less than 80° C. to avoid protein denaturation. A reducing agent is added to improve the flowability during processing. The disadvantage of adding a reducing agent is that most reducing agents are not compatible with animal feed regulations, and therefore the resultant products would be unsuitable for use as an animal chew.
PCT Publication No. WO 00/13521 discloses a protein-based thermoplastic composition comprising, among other components, a protein such as soy protein or wheat gluten and an edible plasticizer. The composition can be formed into a chewable pet toy or artificial dog bone by injection molding, pressure molding, transfer molding or extrusion molding. In this case water is added to improve the processing flowability. During processing the water content of the composition is increased to 35% by weight of the composition. Some of this water is removed downstream of the process by drying the pellets. The disadvantage however of adding water to improve the processing flowability is that this water must be removed downstream, necessitating the requirement of a drying step to remove the excess water which is both expensive and time consuming. Additionally, the high percentage of water added has a disadvantageous effect on the resultant product in that as water evaporates from the product during storage the surfaces of the product crack.
In the process disclosed in PCT Publication No. WO 00/13521, the ingredients are all blended and mixed together at the same time. This is disadvantageous in that the moisture uptake of the protein and thus the overall moisture content is difficult to control thus resulting in the need for an additional amount of water to be added than what is actually required to provide the minimum moisture content necessary to hydrate the protein. Additionally, extrusion molding is carried out at temperatures of between about 95° C. and about 110° C. The disadvantage of using temperatures in this region is that protein denaturation occurs. As the protein denatures, its molecular structure and thus properties change. This results in a product of reduced nutritional value. Furthermore, as the protein in the wheat gluten denatures the wheat gluten adopts a chewing gum like consistency, becomes sticky and is extremely difficult to handle during processing. Additionally during denaturation of the protein the composition containing the protein hardens and forms a shape in the extruder. Further shaping of the composition downstream is therefore difficult.
Thus, there is a need for a process for preparing a product containing wheat gluten suitable for forming into a chewable pet food and a chewable pet food which overcomes the above-mentioned disadvantages.